1. Field of the Invention
The present invention relates to a scanning probe microscope having a mechanism for correcting an inclination between a scan plane of a probe and a sample plane, and a recording and reproducing apparatus having a similar mechanism, and an inclination measurement mechanism.
2. Related Background Art
An SXM collectively refers to a technique to measure a surface status of a sample by scanning a probe on a surface of the sample while detecting various mutual actions which depend on a distance between the probe and the sample. It is a measurement method derived from a scanning tunneling microscope (hereinafter referred to as STM) which utilizes a tunneling current, and it is explained by referring the STM. The STM developed by G. Binning et al. [G. Binning et al., Helvetica Physica Acta, 55, 726 (1982)] utilizes a phenomenon that a tunneling current flows when a metal probe approaches a conductive sample at a distance of approximately 1 nm while a voltage is applied therebetween. Since the current very sensitively increases monotonically with the change of the distance between them, the surface status of the sample can be very precisely detected if the sample is scanned while the tunneling current and the height of the probe are detected.
When the surface status of the sample is observed while the probe is scanned on the sample, either a method for measuring the change of the height of the probe while controlling the height of the probe so that the tunneling current is kept constant (constant current mode) or a method for measuring the change of the tunneling current Jt when the probe is scanned while the height thereof is fixed at a constant level (constant height mode) is used. In any case, it is required that the scan of the probe is parallel to the sample plane. For example, when a crystal of highly oriented graphite (HOPG) is observed, a result as shown in FIG. 1 is to be obtained in accordance with the arrangement of atoms.
However, if the sample is arranged obliquely, the surface shape is observed with distortion. If a range of scan of the probe is relatively small, it may be possible to separate a signal caused by an actual structure of the sample surface by use of electrical filter, but when the inclination is large, it is difficult to observe over a sufficiently wide range. For example, in the constant current mode, continuous measurement is not attainable when a total heightwise displacement of the probe due to the inclination of the sample exceeds a heightwise fine adjustment range of the probe.
When the constant height mode is selected, if the sample is inclined, the probe may be too far away from the sample to detect the tunneling current or the probe may contact to the sample. In order to avoid this, a feedback is applied even in the constant height mode so that the detected tunneling current is maintained within a certain range, and the height of the probe is gradually changed. In such a case, the correction beyond the heightwise fine adjustment range of the probe is not attainable.
Even if it is within the range, as far as the scanning surface (hereinafter referred to as XY plane) direction of the probe and the sample surface (hereinafter referred to as X'Y' plane) direction are not parallel to each other, there exists a difference between a displacement of the probe and a real space distance as shown in FIG. 2. Namely, where an angle defined between the sample surface and the scan plane is .theta., a change in the height due to the inclination is superimposed on the detected signal. Even if a low frequency component due to the inclination of the sample is cut off by an electrical filter as is done in the prior art to extract a signal produced by a periodical structure of atoms, the distance in the resulting signal is compressed by a factor of cos.theta. because the displacement of the probe scans over a length of 1/cos.theta. times on the sample surface. As a result, a distance precision is low, and the larger the observation area is, the larger is a difference between the real space and the scan distance.
This equally applies to the STM which has the same movement mechanisms of the probe and the sample as those of the STM. Further, in a high density recording and reproducing apparatus of a molecule order by using the SXM, the anticoincidence or the antiparallelism between the XY plane and the X'Y' plane lose a precision of recording, reproduction and erasing.
Japanese Laid-Open Patent Application No. 2-147803 proposes an STM having a mechanism for manually rotating a sample in order to solve the above problem, but it is difficult and troublesome to manually conduct such a strict operation.